map. Tufte23 pointed out that triptiks and subway maps similarly distort the shape of routes and eliminate unnecessary detail. Hand-designed destination maps include only the major routes to a location rather than all possible routes. These maps progressively increase the level of detail, showing only the highways far from the destination while including arterial roads and finally the residential roads near the destination. Both route and destination maps typically use multi-perspective rendering in which the roads are drawn in top-down plan view while important landmark buildings are drawn from a side view so their facades are visible.

Although analyzing hand-designed visualizations is often a good initial approach for identifying design principles, this strategy also involves limitations. In some cases it may be tempting to form generative rules that are too specific and do not apply outside the range of analyzed examples. In other cases the rules may be so general it is unclear how to apply them to specific examples. Such difficulties often arise when the perceptual or cognitive rationale behind a particular visual technique is not clear. In the context of route maps, for example, although our analysis revealed that mapmakers often distort road length, angle, and shape, it was not immediately clear how such distortions improved the perception and cognition of route maps.

Similarly, we have found that one
of the challenges in analyzing hand-
designed visualizations is to factor
out differences due to artistic style.
Designers may choose visual attri-
butes (such as font type, color palette,
and line width) for aesthetic reasons
whereby one font may simply look
nicer than another to the designer. Al-
though such aesthetic design choices
are important considerations, the
goal of our analysis is to determine
how the design choices improve the
perception and cognition of the infor-
mation, rather than how these choices
improve aesthetics. The difficulty is
that these design choices often affect
both the aesthetics of the display and
the perception and cognition of the
information; how to separate the two
effects is not always clear.

FIGure 7. unIQue MedIa

Figure 7. a hand-designed tourist map of san Francisco emphasizes semantically, visually, and structurally important landmarks, paths, districts, nodes, and edges, using multi-perspective rendering to ensure the facades of buildings are visible (left). our tourist-map design system is based on these principles and similarly emphasizes the information most important for tourists in this map of san Francisco (right).